The conventional semiconductor device may include a metal oxide semiconductor field effect transistor (MOSFET). This semiconductor device includes a p-type semiconductor substrate, an n-type semiconductor layer formed on the semiconductor substrate, and an n-type drain region and an n-type source region formed to be spaced apart from each other on a surface region of the semiconductor layer.
In the conventional semiconductor device, a drain metal for supplying electric power to the drain region is typically connected to the drain region. Such a semiconductor device is typically designed to have equipotential lines distributed such that the electric field strength becomes uniform from the drain region to the source region in a state in which a drain voltage is applied.
However, in the configuration in which the drain metal is disposed on the drain region, there is a possibility that the equipotential lines extending from the drain metal are sharply bent toward the drain region near the surface of the semiconductor layer to cause a region where the distances between the equipotential lines in the semiconductor layer are narrow, i.e., a region where the equipotential lines are dense. The region where the equipotential lines are dense is a region where the electric field strength is higher than that of other regions and the electric field is locally concentrated. Such a local electric field concentration has a problem that it causes a reduction in withstand voltage of the semiconductor device.